1. Field of the Invention
The present invention relates to a power control apparatus. More particularly, it relates to a power control apparatus for distributing electric power from a power source to each load.
2. Description of Prior Art
A power control apparatus of this kind generally consists of a box-shaped casing in which a plurality of control units are vertically arranged in a multistage and bus conductors for power source are vertically extended. Each of the control units is equipped with at least one line disconnecting device for turning on and off a load circuit to protect it. In the power control apparatus, there is provided a single control circuit being common to the control units, which includes a power circuit, an alarm circuit and so on.
FIG. 1 is a diagram showing a wiring arrangement of a conventional power control apparatus which is applied to a control center in view from the front side. It is apparent from FIG. 1 that the power control apparatus (control center) 10 of this kind is generally placed side by side in a row.
The power control apparatus 10 is generally constituted by a control unit section 14 in which a plurality of control units 12 are arranged in a multistage, a vertical wiring section 16, a horizontal bus conductor section 18 and a general terminal block section 20. Between terminals 30X and 30Y of a power source for the control circuit being common to the control units 12, a contact for turning off at the tripped position of a thermal relay, an ON push-button, an OFF push-button and a coil of an electromagnetic switch (all not shown) are serially connected in this order through an auxiliary contact actuated in association with on-off operations of a line disconnecting device (not shown). A self-holding contact of the electromagnetic switch is connected in parallel to the ON push-button. In FIG. 1, an external push button and a circuit for a signal lamp are omitted. Between terminals 36P and 36N of an alarm circuit, a contact closing at the tripped position of the line disconnecting device is connected in parallel to a contact closing at the tripped position of the thermal relay even though both devices are not shown in FIG. 1. The terminals 36P and 36N for each of the control units arranged in a multistage in a casing of the control center 10 are connected in parallel and are connected to the alarm circuit as a group. Vertical wirings 38 for the terminals 30X, 30Y, 36P and 36N led out from a terminal block in one of the control units 12 are connected to the general terminal block 40. Cross-wirings 42 are provided to connect between terminals in the same general terminal block and to connect between the general terminal blocks 40 of the control centers 10 adjacent each other.
The conventional power control apparatus applied to a control center 10 has encountered the following drawbacks when wiring operations have been carried out for the control units 12 arranged in a multistage.
(1) A number of wiring steps are needed to take a long time for wiring operations to thereby cause delay in an appointed date of delivery.
(2) A space for the control unit section 14 is limited because of the presence of the general terminal block section 20 for receiving therein the general terminal blocks 40.
(3) When a control unit 12 is to be added or to be removed, it is necessary to add or remove the vertical wirings 38 for the specified control unit. In this case, since the wiring operations is carried out after the assemblage of the apparatus, modification and rectification of the vertical wirings in a limited space are extremely difficult.
(4) External cables for a main circuit and a control circuit are vertically extended in the vertical wiring section 16 in addition to the vertical wiring 38. The vertical wirings are previously arranged in the wiring section at the factory, while the external cables are arranged in the wiring section when the control center is at the installation location.
(5) Since a drawing port for vertical wirings 38 led out from the control units 12 and a pulling-in port for the external cables are formed at the same side in the casing, wiring operations are complicated and it is difficult to maintain good condition for the wiring.